Chemokines are inflammatory mediators of the chemotactic and cytotoxic functions of a large variety of cells including neutrophils, monocytes, eosinophils, basophils and lymphocytes. These functions are initiated through interaction with specific cell surface G-protein coupled receptors (GPCRs). Most chemokines activate more than one receptor on leukocytes. The hypothesis that underlies this application is that since multiple chemokines are present at sites of inflammation, the chemokine receptors activities must be tightly regulated to prevent tissue damage. We have developed a cellular model, a rat basophilic leukemia cell line (RBL-2H3), in which chemokine receptors can be singly or multiply expressed to display many leukocytes activities. These studies have provided striking evidence that these receptors cross-regulate each other?s function at multiple steps. Signal duration and protein kinase C (PKC) activation have been shown to be critical for receptor cross-regulation. Studies in phagocytes and mouse models of peritoneal and skin inflammation have shown a complexity of cross-regulation among interleukin-8 (IL-8) and RANTES. This complexity likely reflects the ability of these chemokines to activate multiple receptors in leukocytes. The overall objective of this application is to elucidate the mechanism(s) of cross-regulation among the receptors for IL-8 (CXCR1 and CXCR2) and RANTES (CCR1 and CCR5) and to identify specific molecular targets in the signaling pathways, which modulate their ability to mediate and undergo cross-desensitization. Mechanisms of cross-desensitization will be investigated by determining the role of different protein kinase C (PKC) isozymes in receptor cross-phosphorylation. The hypothesis that arrestin-mediated receptor internalization modulate signal duration will also be tested in beta arrestin deficient mice. Chemokines are involved in many acute and chronic inflammatory diseases such as rheumatoid arthritis, emphysema, cystic fibrosis, chronic bronchitis and bronchiectasis and proliferation of tumor malignant melanoma cells. Understanding the molecular mechanisms governing the regulation of chemokine will aid in understanding the control of inflammation as well as the etiology of many inflammatory disorders. These studies will also identify specific targets for the development of therapeutic drugs for the modulation of inflammation.